The present invention relates to a polyester composition, and more in detail, the present invention relates to a polyester composition for producing shaped articles which are excellent in mechanical properties such as impact strength, tensile strength, bending strength, etc. and show excellent appearance and colour tone. Of the polyester composition according to the present invention, particularly those containing a carbodiimide compound are the useful polyester composition in the field where dimensional-stability of the shaped articles such as automobile connectors is demanded because of the hinge-resistance property of the carbodiimide-containing polyester composition.
Since the thermoplastic polyester represented by polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc. is excellent in mechanical properties and heat-resistance as well as in dimensional-stability, the thermoplastic polyester is utilized as the material for automobile connectors, electric connectors or electronic connectors.
By the way, in the case where the automobile connector knob made of polyamide is used, there is a danger wherein the connection of the connector becomes loose and comes off by the vibration of the automobile or the dimensional variation of the connector. Accordingly, the polyesters favorable in the dimensional-stability, such as polybutylene terephthalate, have attracted attention of persons skilled in the art. On the other hand, as a counter measure to the vibration during the covering of the automobile, it has been considered to additionally attach a rock-mechanism utilizing a hinge to the connector. However, there is a problem of breaking of the thus attached rock-part, because the ordinary polyester is poor in the hinge-property.
Namely, the polyester of the improved hinge-property has been demanded.
Hitherto, as a method for improving the impact strength of the polyester, a method of adding a modified copolymer of ethylene and an .alpha.-olefin by grafting an .alpha.,.beta.-unsaturated carboxylic acid to the copolymer, or adding an acrylic rubber to the polyester has been known, and in addition, a method of adding a random copolymer having functional groups adherable to the matrix (i.e., the polyester) with the polyester has also been known (refer to Japanese Patent Publication No. 59-28223 (1984)).
Furthermore, a method has also been known for improving the tensile strength and the bending strength of the polyester, wherein an inorganic filler represented by glass fiber is added to the polyester.
However, in the case of adding both the above-mentioned random copolymer and the glass fibers to the polyester, although the impact strength, the tensile strength and the bending strength of the thus produced resin composition are improved, respectively, the impact strength of the resin composition is inferior to that of the resin composition with which only the random copolymer is added, and the tensile strength and the bending strength of the thus produced resin composition are inferior to those of the resin composition with which only the glass fibers is added.
As a result of the present inventors' studies for improving the mechanical properties of the polyesters, the present inventors have obtained a finding that the impact strength, tensile strength and bending strength of the polyester can be simultaneously improved by adding a modified copolymer of ethylene and an .alpha.-olefin prepared by grafting a specified compound with a copolymer of ethylene and .alpha.-olefin, with the polyester, and that a more excellent effect is obtained by adding, in case of necessity, an epoxy compound, a carbodiimide compound and an inorganic filler to the polyester in addition to the modified copolymer, and the present invention has been attained on the basis of the present inventors finding.